BRYOZOANS are colonial animals that live in both freshwater and seawater. A colony is composed of hundreds of very tiny individuals, each of which has a special organ that filters small food particles from the water. Bryozoan colonies are attached to the seafloor or to other organisms. Colonies of different species have a variety of shapes, including fans (figure 1b), discs (figure 3) and bushes (figures 2, 4, 5, 6).
At least seven species of bryozoans lived in the Silurian reefs of Wisconsin, and six of these species are shown in the diorama. Disk-shaped colonies, which grew over loose sediment and other organisms, represent reef binders. Fan and bush-shaped colonies represent dwellers, and where they were abundant and closely-packed, they may also have functioned as bafflers.